Means for continuously forming thin plastic sheets



H. WARP June 3, 1952 MEANS FOR CONTINUOUSLY FORMING THIN PLASTIC SHEETSFiled Oct. 21, 1946 I 'P;NVENT0R. Zia 270M 11/0 20, BY

Patented June 3, 1952 MEANS FOR CONTINUOUSLY FORMING THIN PLASTICSHEETS:

Harold Warp, Chicago, Ill., assignor to Flex-- Glass, Inc'., acorporation of Illinois Application October 21, 1946, Serial No. 704,648

1 Claim. 1

The invention relates generally to means for forming a thin,plate-glass-clear sheet of plastic and, more particularly, aplate-glass-clear and embossed thin sheet of plastic.

There is a present and long unfulfilled demand, despite feveredresearch, for a thin sheet of one of the plastics which sheet has the.smooth surfaces and the clarity of 7 plate glass. Many thin sheets ofplastic are now on the market which are highly transparent and whichwhen applied over a package appear very clear and smooth to the laymanand the ordinary observer. However, it is recognized by those skilled inthe art that these sheets now on the market are not truly transparent.In fact, even the layman can detect this fact by taking such a plasticwrapping from a package of cigarettes or the like and looking throughthe same at a distant object. When so viewed, the sheet will .beobserved to have a multitude of minute parallel lines and the light rayspassing through the sheet will be diffused as noted by a blurring of theoutline of the object.

It is a primary object of the invention, therefore, to provide a meansfor producing thin sheets of plastic which are truly transparent.

Another object is to provide an apparatus for molding a thin layer ofplastic in a moldable state into a thin sheet of plastic with desiredareas of both sides of the sheet mirror smooth and operable to retainthe molded plastic in the desired form until set, all while the sheet iscontinuously fed through the apparatus.

It is also frequently desirable that a thin sheet of plastic, i. e., asheet on the order of .004 of an inch thick, be provided with raised orembossed strips or areas while still remaining transparent and smoothsave for the margins of the raised areas. These embossed and thickenedportions of the sheet may be solely for the purpose of reinforcing thesheet or they may be solely for ornamental purposes, or they may serve acombined reinforcing and ornamenting function. The production ofembossed, thin sheets of plastic on a commercial basis like plain thinsheets has long been sought unsuccessfully.

It is another object of this invention, therefore, to provide means forproducing a thin, embossed sheet of plastic in a convenient and facilemanner.

Still another object is to provide a means for producing a thin embossedsheet of plastic having surfaces free of minute lines or ripples whichreduce transparency.

A further object is to provide an apparatus for forming plain orembossed, thin sheets of plastic having means including an endless beltforming molding means for plastic with the endless belt serving to holdthe molded sheet in molded form until it has set.

Other objects and advantages will become apparent from the followingdetailed description taken in connection with the accompanying drawings,in which:

Fig. 1 is a side elevational view in more or less schematic form of anapparatus embodying the features of this invention. To make anydetectable showing of the sheet, it appears many, many times normalthickness and is, of course, greatly out of proportion to the balance ofthe figure.

Fig. 2 is a top plan view of a portion only of the machine of Fig. l,the figure being on a larger scale than Fig. 1, and the sheet beingshown in broken outline.

Fig. 3 is a transverse sectional view taken along the line 3-3 of Fig. 2of the main molding wheel.

Fig. 4 is a longitudinal sectional view, very greatly enlarged, of aportion of the finished sheet.

While the invention is susceptible of being practiced by various methodsand by altered or modified apparatus, a preferred method and means willhereinafter be described. It is not intended, however, that theinvention is to be limited thereby to'the specific disclosures made. Onthe contrary, it is intended to cover all modifications and alternativeconstructions falling within the spirit and scope of the invention asdefined in the appended claims.

Turning first to the method, the plastic of which the sheet is to bemade is first dissolved (solution) or suspended (dispersion) in somesuitable carrying medium. A layer of this carrying medium havingsufiicient quantities of the plastic dissolved or suspended therein isthen spread upon or laid upon a suitably formed sur-' face. This surfacemay be perfectly plain if the side of the finished plastic sheetincontact therewith is to be plain, or it may be formed with grooves orother depressed areas if the finished sheet is on that side intended tohave a raised configuration, that is, embossing. Whether plain or formedwith grooves or depressed areas, the surface is polished to give amirror smooth surface to the finished sheet. The layer of material, thatis, carrying medium and plastic, is then subjected to a controlledatmosphere which reduces the material to a consistency suitable formolding and such reduction of the material may be accomplished in one orin a plurality of steps or w 2,598,866 7 3 4 stages, as desired. Wherethe material is a respectively at the front and rear of theapparasolution, this step or stage involves driving oil tus. Drums I4and I5 are, for purposes herethe excess solvent and, Where the materialforminafter more fully described, positioned on oping the layer is adispersion, this step involves an posite sides of the drum II. Asclearly seen 7 absorption of the plasticizer forming the carry- 5 inFig. 1, the belt III runs over the end drums ing medium into theparticles of plastic, a phe- I2 and I3 and partially around the drumsI4, nomenon known to those skilled in the art. In H and I5 in aninterlaced manner, that is, over either event; thelayer of materialbecomes a the drum I' l, under the? drum 'I I,and again overhomogeneous, semi-solid mass capable of flow- "the dum I5.Naturally'supplementing the large ing, that is, of being molded underpressure. drums II to I5, inclusive, are at least a pair of Usuallythese steps involve a raised temperature, small rollers I6 and I! whichserve primarily that is, one above ordinary'roomtemperatures, :toguidethe endless belt I0. One of these, namethough it is conceivable that thedriving ofi :of sly, roller I6, is disposed beneath the drum II th solvnt or th a s rpt of th plesticizer while the roller His disposed just inadvance might be accomplished in other ways. 5 0f theLdru'm I2,"considered in the direction of When the plastic, nowdepositedbfitheformed' movement or the belt. Note that all of thesurface in the form of a r'elatively r tliin sheetj drumsand rollerssavethe roller II (drum II or film, is in the moldable state above menismaintained out of contact with the belt II! by tioned, a second surfaceis applied tothe pthe layer of material) contact the interior surpositeorfree face or side andsufficient pressure face only of the belt. RollerI'I, therefore, applied to cause the-*plastic to fioW- 0ut to the{should be made of a 'material that will not mar -desird 1thicknessdetermined by -spaeingpf the the polishedflexternal surface or belt I 0.'llo obsurfaces-and also to flow into any grooves or tainthe necessarypressure between tlie erfdless other depressed areas that maybepresentsoas belt II] and the drum- I.I, the;belt mustyof cou'rse, toassume the'configur'ation desire'di' 'Tliis-second be held taut. T-hed'egree 'of tautness may be surface, like *the first," may be-" ei'therplain or v'aried either by: adjusting the roller 'l fi tdw'ard 'iormed-with grooves or depressed ar'eas but in or fromthe drum- I I- or by-adjusting 'the dnum any event should be polishdso}as" to' provide a Vlilongitudinally of-ithe apparatus, malde possible "verysmoothsurface*with-vvhich the layer of by adjustable bearings I8 inwhichthe drumi l3 materialis-in contact. when thus 'held between isjournaled. 7 the surfaces' whichact asmolds or dies and 3 Means isprovidedfor layln'gL-on the?beltft0tat *Which} rn'or-emer,"are to be 7distinguished from the drum I2 a thin" layer I9 of the material "mereline conta'ct of -a pairof-squeeze rollers or which is to :be'-molded:intothe' thinishet. L'This *thelikefthe material is subje'cted, ifnecessary, iayer 0f material mayfbe appliedeither aseas'sowinch willcause the plastic toset in the-configdium for. the plasticDETtlCIBSJQILaS a dispersion ;uraticn tvhich it then has. Itwilllee-understood with a plasticizerr constitutingthe *carryingiiimethatthe nature-of the-temperature change' will Ilium for the. plastici'particles. Theihrieariszfor vary with the character of the-' m'ater-ial;an 'a'pplying thelayer is not critical tothistinvenincrease 'in'temperature if the ma'trial isther-s tion and the layer 'ofxmaterial"may: be if'edi onto -mosettin-g;-a-'-decrea'se if the material is-'thermothebelt-as by a -hopper or the drum' IZLmay cause -plastic.-1After *the plastic has set and "only -tl*1ebelt I0=to dip intozl'az'bathofthe'imaterial after it has taken la firm-set,' --the formed and thuspickiupaalzsufficient'layerpf?tliei'inasheet is removed from between thesurfaces terial to formithe"thin-sheet. 'Hereinw a bath forming them'olds or dies vi and is rolled- 20 0f materialis-illustratedewith"the"drum' flso -for furth'er "treatment or forshipment; fIt disposed as to 'havetits periphery'belowithe level "is tobe noted that' the -'metl od'i involves the of thematerial'inthe;bath-:so that theablttwill steps iof molding the plastic intoa thinsheet pass through 'the 'material. To thate'ndpzthe arid holdingtheplastic under' pressure and in roller I'I'is' mounted'onithe"leadingedgetofthe its molded:" fo'r-in until the plastic has taken ab'ath,consideredz'iin the:direction bf 'movement -permanent-js'et andmdlon'gerhasf any teri'dency of' the'belt: I0, soras'sto' lift" the belt overthei-edge 'toj'resume-f somej earlier or different form. of thebath'While theItrailingJedgeiof:thei'bathiifi lviea-ns is provided forcarrying cut' the method is 'provided' 'with: :ardoctorsblade -2 I-'mounted for v in a facile and-continuous manner. -To that iajustmentztowardfandfrom:the drum' I-2 ='so-:as

end, there is provide'dan apparatus l-raving ato:determinethethicknessof the'layer:-of ,-=ma- 'pair or means-providingendless moving surfaces terial that pp e'beltwhich for a portion oftheir movement are Interpose-dfbetweenathetdrum'-I-2r'withitsibathbrought andheld-closelyadjacent to one ano'ther -'2il andthe'idrumsllrl, ldeand I:5:'are"'a plurality in a: manner? permittingmolding-'pressure to be o e ein twofi controlled atmospherewham rapplied thereby to any materialinterposed thereh s ar h r d ematically-showmand between. I Such 'endless moving 1 surfaces might ared d to ep l ly-different st p conceiv'ablyf' bef provided by a pair'ofbelts- "or by r n the-method, zand-aindividliallywcona belt and --a drHmor roller-of substantial ditrolled chambersi of' the apparatu W r-eathe"ameter -about atlea'st-a portion'of -which the carryi g medium-i r f lvn ff x raction fifrthe belt curves,'or conceivablyeven by othermeans.'-' Carrying l 'n*" QQIIIT B, 8 -vaporizin Hereinf'by'-way-'of-*example, there is disclosed ss'a dis:pre e ablv o d ot d westages an apparatus embody-ing the elements of' the with themajority'-ortheso vent-d v nofi second-mentioned arrangement; namelyy-ane'nd- Iapmication fh eh r mp r ur :t0 m

-less-beltyI0*and "a; dru r bn 'ifl bf 1arge rial and large volumes ofair flow acrossthe diameter about a portion of which -the 'belt is'70'material asiitip usha hefirstofsthe two caused "to curve. *As a matterof -'-fact, the apchambers 'vvherej provision; isnmade foreregoveryparatus gmplgysfourwlarge d m -H wofwthe largeiamounts zof --solventthatwill be I 3, -l4- and 'I-5'-'in"-adclitiont0 the drum- II. 01 drivenoff. It will be appreciatedzt'hatithersolvent these, drums-l2f-and- I-3-determine' -the' -e'xtreme shouldnot'be driven ofi at suchzaraterastocause "limits of the path of the belt *I I), being" locatedabbilingth r f F for "bubbles migh then fbe to, a further temperaturechange of a character; :l'ution employingi-.a solvent-::as1thecarryingzmetrapped in the sheet. While passing through the second of thetwo chambers 22, additional solvent may be driven off and thetemperature of the material further raised converting the material to asemi-solid but still flowable and moldable state. Where the layer I9 ofmaterial is a dispersion, the reduction of the material to a semisolidstate is a combined process of absorption of the plasticizer into theparticles of the plastic and a fusing or blending of the particles intoa homogeneous mass. Thus as the layer of material passes through thefirst of the two controlled atmosphere chambers 22, the temperature ofthe material is raised to bring about the absorption of the plasticizerinto the particles of the plastic, as well known to those skilled in theart, and to initiate fusion of the particles while the temperature ofthe second of the chambers 22 serves to complete the fusing or blendingprocess.

The drums I I, I4 and I5 are mounted in a third controlled atmospherechamber 23 and, in addition, one or more of the drums I I, I4 and I5 maybe individually controlled as to the temperature of various partsthereof. Typical of the construction which the drums II, I4 and I5 mayhave is that shown for the drum I I in Fig. 3. The drum Ii, of course,has end walls 24 and a peripheral wall 25. Extending axially of the drumI I and nomotatably within the drum is a cylinder 26 having spider-likepartitions 21 extending radially therefrom into substantiallyfluid-tight engagement with the inner surface of the peripheral wall 25.In this way, the cylinder 26 with its spider-like partitions 21 dividesthe drum into a plurality of compartments 28, 29, 30 and 3!, forexample. Extending longitudinally of the drum just outside of thecylinder 26 are a plurality of pipes 32, 33, 34 and 35 adapted tocommunicate through small openings formed therein throughout the lengththereof with the chambers 28, 29, 30 and 3|, respectively. Similarlyextending longitudinally of the drum but near the periphery rather thannear the center thereof are pipes 35, 31, 38 and 39, again located,respectively, in the chambers 28, 29, 30 and 3I and having small radialopenings throughout the length thereof. The pipes 32 to 39, inclusive,are all adapted at one end to extend radially into the cylinder andthence outwardly of the drum II through one end thereof within thejournal in order that they may remain stationary while the drum rotatesrelative thereto. These pipes are then connected to sources of fluidmaintained at different temperatures with the fiuid preferably beingsupplied to-the chambers through the .pipes 32 to 35, inclusive, andwithdrawn from the chambers through the pipes 36 to 39, inclusive. Inthe particular embodiment here shown and with a thermoplastic material,the chamber 28 is heated While the chambers 29, 30 and 3| are maintainedat successively lower temperatures in order to cause the material totake a set before it leaves the space between the belt I and the drum Asabove indicated, the drums I4 and I are,

.plastic, that is, thermosetting or thermoplastic,

and thus may be either higher or lower than the temperature of that.portion oi. the drum II immediately adjacent the drums I4 and I5. Inthis connection, one precaution must be exercised, particularly when athermoplastic material is being molded, and that is that the drum I I atthe point where the sheet I9 is to peel off the drum is at a temperaturelower than the belt I0 at that point in order that the plastic sheetwill, in well known manner, adhere to the surface of higher temperature,herein the belt, and peel off the drum I I. This is for several reasonsnot difficult of attainment even should the drum I5 be at a materiallylower temperature than drum I I. The belt I0 after all does not contactdrum I5 until the critical point is reached, the layer of plastic tionfirst to mold the sheet to its desired form and then to retain the sheetin its molded form until it has taken a permanent set while at the sametime obtaining a continuous production of the sheet, the drum II, atleast, is of large diameter 'so as to provide a large surface, measuredlengthwise of the belt, with which the belt may be associated for thenecessary Iperiod of time to carry out the above named essential stepsof the invention. To further that end, the drums I4 and I5 should be solocated that in passing over them and under the drum II the belt willcontact a goodly portion of the periphery of the drum II. Herein thedrums I I, I4 andIB are so located that their axes lie in a common planewith the belt Ill thus contacting 180 of the periphery of the drum II.It is conceivable, however, that the drums I 4 and I5 might be locatedhigher or lower than shown in Fig. 1 so as to cause the belt to contactmore or less than the half of the circumference of the drum II nowcontacted. To

determine and vary the thickness of the sheet that will be obtained, thedrums I4 and I5 should be adjustable relative to the drum II so as tovary the clearance between the belt I0 and the drum I I as it passesthereover. To that end the drums I4 and Bare journaled in bearings Mwhich are adjustable to. vary the spacing between the drums I4 and I5and the drum II where they are tangent to one another.

interposed between the controlled atmosphere chamber 23 and the drum I3is a fourth controlled atmosphere chamber 42 through which the belt I0and the now formed sheet I9 pass. The atmosphere in this chamber will besuch as to cause a completion of the setting of the material and areduction of the material to its final and permanent form This mayinvolve further cooling of the sheet I9 or it may involve a raising ofthe temperature of the sheet to effect a curing operation, or it may bea combination'of or a compromise of those extremes.

Because of the extreme thinness of the finished sheet I9, it must becarefully handled and particularly the removal of the sheet from thebelt must be carefully done. Herein the finished sheet is wound on aroll 43 which is herein shown located near the front end of the machine.To aid in peeling the sheet off the belt, there are positionedunderneath the belt and at a point somewhat beyond where the finishedsheet is peeled from the belt a plurality of air nozzles 44 from whichjets of air are directed ue Yasa n tt e t I", 1

ness and, if the sheet is to be embossed, into the desiredconfiguration. Where the sheet is to be embossed, the thickness of thelayer l9 will be sufficiently greater than the thickness of the finishedsheet so that there will be excess material which will be forced intothe grooves, recesses or depressions formed in the faces of the belt andthe drum ll. Having been molded into the desired shape, the sheet is notreleased as has been the past practice, but it is, on the contrary, heldbetween the belt and the drum II for a considerable period of time andis, moreover, held in the same configuration initially given it. Whileit is thus held between the belt and the drum II, it is as it passesaround the drum subjected to different temperatures, hereinprogressively lower temperatures. These temperatures are such that thesheet is permanently set before it reaches the point where the beltcurves away from the drum I l and runs over the drum 15. Because thedrum ll, particularly at the chamber 3|, is at a low temperature,specifically at least lower than the temperature of the .drum IS, thesurface of the drum II at that point will be at a temperature lower thanthat of the belt I and thus, as is characteristic of plastics, the sheetwill adhere to the belt and readily peel off the drum II and be carriedby the belt through the chamber 42 around the drum I3 and forwardlytoward the front of the machine. Upon reaching the roller 43, thefinished sheet I 9' is wound onto the roller 43. To aid in peeling thesheet from the belt without tearing, jets of air from the nozzles 44 aredirected against the belt at the line of severance of the sheet from thebelt.

It is believed apparent from the foregoing that I have perfected amethod and apparatus for forming truly transparent sheets of plastic ina continuous operation. The sheets are free from ripples or lines whichtend to interfere with the true transparency even though those lines orripples are not generally realized as present in present day, thinplastic sheets except by those working in the art and by the laymanafter he has been apprised thereof and the interference with thetransparency pointed out to him. With my method and apparatus, moreover,the sheets may be either plain or embossed on one or both sides, asdesired, and with the embossing taking any degree of intricacy desiredfrom simple reinforcing ribs to very intricate lace or fiower patterns.The thickness of the sheet is readily ticularly, a synthetic polymer orcopolymer and is not employed as an adjective indicating a certain stateof a material.

Similarly, the term polished surface" is intended to mean generally avery smooth surface which normally is obtained by rubbing or polishing,but it is not necessarily limited to attainment by those methods but isintended to cover an equally smooth surface which is attained simply byflowing a material over a surface if there is any such material which iscapable of flowing and setting with such a finish.

I claim as my invention:

An apparatus for continuously forming a thin, transparent,polished-surface sheet of plastic comprising, in combination, a firstmeans providing a movable, endless surface, a second means providing asecond movable, endless surface, said surfaces moving at the same linearrate in paths which over a significant portion thereof are closelyadjacent and consistently uniformly spaced to form moving andcooperating dies for molding plastic received therebetween and forconfining the plastic under pressure for a predetermined time in theshape into which it has been molded until set, means for applying alayer of plastic in a fluid state to one of said surfaces, a controlledatmosphere chamber through which said surface having the layer ofplastic passes disposed between the pointof application of a layer ofplastic and the approach of said surfaces into close proximity to oneanother and acting on the layer of plastic to convert the layer to amoldable layer of plastic, and means for altering the temperature of theplastic while confined between said surfaces and between the time theplastic enters and leaves the space between said surfaces to cause asetting of said plastic.

HAROLD WARP.

REFERENCES CITED The following references are of record in the file ofthis patent:

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